No description available.

This thesis makes use of the intermediate energy R-matrix approach (IERM) in computationally modelling various single and double ionisation processes. The basis used in the IERM approach is an ideal candidate for representing a double electron continua in a time-dependent or time-independent, general N-electron R-matrix code and one of the main objectives of the thesis is to explore the efficacy of the basis used in the IERM approach in representing a double-electron continua. To do this, the IERM method is applied to the study of photoionisation and photo-double-ionisation of various He-like and Be-like atoms and ions in the ground and excited initial states, and preliminary calculations of electron impact excitation involving high lying energy levels of H is investigated with the two-dimensional R-matrix propagator package. The convergence of the basis for these processes is examined. Throughout the thesis the results obtained with the IERM method are compared to experimental results and those from other state of the art theoretical approaches, and agreement is excellent in all cases. In the case of He-like and Be-like atoms and ions, trends in moving along the isoelectronic sequences and between the ground and various excited states are analysed and compare well with existing models where available. The data presented is also of use in astrophysical applications, to experimentalist and to other theorist who wish to study these or similar systems. The IERM basis is shown to be capable of representing a double electron continua and directions in which further work in this field could take are highlighted.

The subject matter presented in this thesis concerns the structural and dynamic studies of new fluorescent probe molecules and the application of polarised fluorescence techniques and analysis to molecular motion, order and solvation in a highly ordered environment. Chapter 1 reviews recent group research providing a context to the work in this thesis, whilst Chapters 2 and 3 concern the study of fluorescent probe dynamics. Time resolved photoselection techniques were used to probe the order and full angular motion of Coumarin 6 and Coumarin 153 in the nematic and isotropic phases of the liquid crystal 5CB. The uptake of coumarin molecules into this host differs from previously studied (Xanthene) probes - in particular, Coumarin 6 is seen to adopt a disruptive position within the alkyl tails due to its size and hydrophobic nature this is discussed in Chapter 2. Furthermore, Coumarin 153 undergoes a substantial increase in dipole moment upon electronic excitation this led to a unique study of time dependent solvation dynamics in both a globally and locally structured environment. The presence of strong solvent- solute interactions necessitated the development of a new approach to the analysis of time resolved polarised fluorescence in ordered systems. This approach and the study of time dependent solvation dynamics in the isotropic and nematic phases of 5CB is presented in Chapter 3. Structural studies of new two-photon fluorescent probes in collaboration with CNRS Rennes and Los Alamos are described in the final two chapters. Large two-photon resonances in the green-visible were observed together with a fuller characterisation of those in the near IR. Polarised two-photon absorption and anisotropy measurements were used to examine the structure of the two-photon resonances. Finally, the stimulated emission depletion dynamics of a branched two-photon fluorophore were investigated and found to differ markedly from conventional (non-degenerate) fluorophores.

A direct measurement of the W boson total decay width is presented in proton- antiproton collisions at y/s = 1.96 TeV using data collected by the CDF II detector. The measurement is made by fitting a simulated signal to the tail of the transverse mass distribution in the electron and muon decay channels. An integrated luminosity of 350 pb_1 is used, collected between February 2002 and August 2004. Combining the results from the separate decay channels gives the decay width as 2.038 0.072 GeV in agreement with the theoretical prediction of 2.093 0.002 GeV. A system is presented for the management of detector calibrations using a relational database schema. A description of the implementation and monitoring of a procedure to provide general users with a simple interface to the complete set of calibrations is also given.

This thesis is an investigation of the breakup of 70MeV polarized <SUP>7</SUP><i>Li</i> on a 120<i>Sn</i> target. The reaction of primary interest is the breakup of <SUP>7</SUP><i>Li</i> into an α and a <i>t</i>. The analysing power ^T <i>T</i>_20 has been measured for this reaction for angles ranging between 9^o and 25^o. The data between 9^o and 15^o was found to agree with a semi-classical calculation for ^T <i>T</i>_20 which assumed that λchar61 1 for the breakup. This implied that at these angles the direct breakup reaction is a Coulomb one. This method of investigation of the reaction mechanism is an improvement on the previously used method of measuring differential cross sections. Analysing powers are inherently more sensitive to measures of deviations from assumptions that are made in reaction models and should therefore enable a more accurate test of the mechanism in question than differential cross sections would allow. The greatly reduced possibility of systematic errors and the requirement of relative rather than absolute yields are also major advantages of analysing powers over differential cross sections. The analysing powers of the sequential breakup of ^7<i>Li</i> and the transfer breakup reactions ^120<i>Sn</i>(^7<i>Li</i>,αchar43 <i>d</i>)^121<i>Sn</i>_g.s.,0.06 and ^120<i>Sn</i>(^7<i>Li</i>,αchar43 α)<SUP>119</SUP><i>In</i><SUB>g.s.,0.31</SUB> were also measured. A comparison of the sequential breakup data with a semi-classical calculation did not provide any evidence for a Coulomb dominated process. Calculations do not at present exist for the transfer breakup reactions, but qualitative explanations of the sign and angular distribution of the analysing power <SUP>T</SUP><i>T</i><SUB>20</SUB> have been proposed.

No description available.

In an excited atom, we have observed, the phenomenon of light emission; and by analyzing the spectrum of the light emitted., we learned. how the atomic electrons behave around the atomic nucleus. Similarly, in the case of an 'excited nucleus', we also observed that there are radiations emitted. Yet, they consist of various different kinds of particles besides photons, e. g.: alpha-particles, deuterons, protons, neutrons, electrons, mesons, etc.. Usually the energy involved is much greater than that occurs in the case of atomic radiation. It is obvious that if we want to form any picture of nuclear structure, certainly first we have to analyze the nuclear spectrum in the same way as we did in studying atomic structure, i. e, to measure the energy values of the individual radiations respectively and to find the relations between them.

A comprehensive series of radioactive source, accelerator-based and reactor-based experiments to determine the structure of some 40 heavy nuclei beyond mass value 100, especially on the nucleus <SUP>168</SUP>Er, is described in the first two Sections of the thesis. In Section I the results of an extensive measurement programme on <SUP>168</SUP>Er involving (n,γ) and (n,e<SUP>-</SUP>) reactions, and single- and two- nucleon transfer reactions, are described. The neutron capture studies were conducted on the curved crystal-, beta-, and pair formation-spectrometers at the High Flux Reactor of the Institut Laue-Langevin, and the particle transfer experiments at the Mcmaster University Tandem Van de Graaff accelerator. The final level scheme deduced from all experiments incorporates the 128 levels identified into 37 rotational bands (for 4 of them, just the bandheads), making <SUP>168</SUP>Er arguably the most fully characterized nucleus known. An IBA model interpretation of the collective states and decay patterns reproduced the observed level scheme well, especially predicting the observed preferred γ-decay from the β- to the γ-band. A discussion is given of various, often competing, theoretical treatments which these experimental results triggered. The results of the large body of particle transfer data from the experiments compared very favourably with the predictions of the Soloviev model. Section II comprises radioactivity studies of isotopes in the actinium chain carried out at the University of Manitoba; in-beam γ-ray spectroscopy of high spin states in rare earth nuclei following (α,xn) reactions performed at the Kernforschungsanlage Jülich cyclotron; and neutron capture studies on heavy nuclei carried out at the Institut Laue-Langevin. Significant advances from the cyclotron experiments included many of the first examples of the "backbending" effect of the nuclear moment of inertia at high spins in nuclei around A=160 and interpretation of observed regularities in the γ-ray spectra in both odd-A and even-A Hg isotopes in terms of the rotational alignment model.

A Gas Proportional Scintillation Detector has been designed and developed. In contrast to other designs, the present G.P.S.D. displays good energy resolution with respect to a-particles and fission fragments over a 2w ateradian acceptance angle, while maintaining the fast timing characteristics of a conventional gas scintillator. The principal problem to be overcome was that of obtaining a uniform light collection efficiency over an extended volume. This has been achieved by the application of a non-uniform electric field to enhance the light output in the regions of low light collection efficiency such that a uniform secondary scintillation response is attained. An empirical expression has been derived to describe the light output as a function of electric field and gas pressure. Analysis of the secondary scintillation pulse shape enables the orientation of the particle track within the counter to be deduced, thus allowing angular distribution measurements to be made. The G.P.S.C. in association with a conventional solid state E-AE telescope has been used to investigate the ternary fission of 252Cf. Measurements have been made of the energy and complete angular distributions of the long range 3H, 4He and 6He emission. Where possible, comparisons have been made with previous data which confirm the viability of the novel technique employed in the present measurements. The data has been extended to provide an essentially continuous measurement over the complete angular range and include the so-called 'polar' emission. The data does not provide conclusive evidence to suggest that the 'polar' emission process is the same or different from the 'normal' ternary emission process. Suggestions have been made to further extend the range of the measurements and also to improve the performance of the G.P.S.C. The electronic circuit constructed by the author to provide control of and data collection for the experiment is discussed in the appendix.

Measurements of the (gamma,pi⁺) reaction on both CH2 and ⁶Li targets were conducted by the Edinburgh, T\”ubingen and Glasgow university nuclear physics groups at the Institut f\”ur Kernphysik, Mainz, as part of the A2 collaboration. The 855 MeV beam from the MAMI-B electron accelerator was steered onto a 4 micron nickel foil radiator creating Bremmsstrahlung photons which were tagged by the Glasgow tagging spectrometer. A Microscope Tagging Spectrometer was used in parallel with the Glasgow tagger to improve photon energy resolution from 2 to 1 MeV. A system of pion detection and identification was developed using Edinburgh’s new ‘ge6 array’; stacked germanium telescopes with pairs of double sided strip detectors (DSSDs) front mounted for vertex reconstruction at intermediate angles.  This allowed data to be taken with greater angular and energy resolution than previous A2 experiments. Data was analysed for incident photons in the range E_gamma = 180 – 220 MeV, at lab angles of 45, 2’ 55, 65, 75, 100, 125 and 150 degrees. The total resolution of the system of detectors (1.2 – 1.8 MeV) was sufficient to separate the ground and first excited states of the 6he nucleus. The differential cross sections for ⁶He were measured relative to the hydrogen cross section which was determined using the MAID2003 code. Comparisons for the ⁶Li(gamma,pi⁺)⁶He_gs reactions were made with recent Plane Wave Impulse Approximation (PWIA) calculations and good agreement was found at small and intermediate angles, however the calculations were not found to give an accurate description of the reaction at larger angles.